Add "unknown" status for noise estimation.

Change-Id: I0fe95332ccfa2e1ad2a01a8e7ddd631289e0f8eb

vp9/encoder/vp9_encodeframe.c

diff --git a/vp9/encoder/vp9_encodeframe.c b/vp9/encoder/vp9_encodeframe.c
index 1606b16..89f2bd9 100644
--- a/vp9/encoder/vp9_encodeframe.c
+++ b/vp9/encoder/vp9_encodeframe.c
@@ -496,7 +496,7 @@
         threshold_base = 3 * threshold_base;
       else if (noise_level == kMedium)
         threshold_base = threshold_base << 1;
-      else if (noise_level < kLow)
+      else if (noise_level == kLowLow)
         threshold_base = (7 * threshold_base) >> 3;
     }
     if (cm->width <= 352 && cm->height <= 288) {

vp9/encoder/vp9_noise_estimate.c

diff --git a/vp9/encoder/vp9_noise_estimate.c b/vp9/encoder/vp9_noise_estimate.c
index 4befbb0..6e717e5 100644
--- a/vp9/encoder/vp9_noise_estimate.c
+++ b/vp9/encoder/vp9_noise_estimate.c
@@ -25,7 +25,7 @@
                              int width,
                              int height) {
   ne->enabled = 0;
-  ne->level = kLowLow;
+  ne->level = kUnknown;
   ne->value = 0;
   ne->count = 0;
   ne->thresh = 90;
@@ -83,7 +83,7 @@
 }
 
 NOISE_LEVEL vp9_noise_estimate_extract_level(NOISE_ESTIMATE *const ne) {
-  int noise_level = kLowLow;
+  int noise_level = kUnknown;
   if (ne->value > (ne->thresh << 1)) {
     noise_level = kHigh;
   } else {

vp9/encoder/vp9_noise_estimate.h

diff --git a/vp9/encoder/vp9_noise_estimate.h b/vp9/encoder/vp9_noise_estimate.h
index 826d125..2663262 100644
--- a/vp9/encoder/vp9_noise_estimate.h
+++ b/vp9/encoder/vp9_noise_estimate.h
@@ -24,6 +24,7 @@
 #endif
 
 typedef enum noise_level {
+  kUnknown,
   kLowLow,
   kLow,
   kMedium,